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How Important Is Your Thumb? Susan S. Plati Topic The opposable thumb Time 30 to 45 minutes Safety Please click on the safety icon to view the safety precautions. Be ! careful when wrapping your thumbs not to wrap them so tightly that your blood circulation is cut off. Do not use any breakable objects.

Materials pair of pants with button at waist objects of various sizes and shapes shoes with laces chopsticks straight-back chair marking pen

pencil and paper large piece of paper assorted coins article of clothing with a zipper plastic drinking glass

Procedure You may need a helper for the second part of this experiment. 1. Observe your hand. Notice especially the relationship of your thumb to the rest of your fingers and the rest of your hand. Note that your thumb can move in a number of directions and angles. 2. Perform the following list of tasks as you normally would, using your thumb and fingers. Pay special attention to your thumb and its involvement in these tasks. Enter your observations on the data table about whether it was difficult or easy to do each task and what the level of “thumb involvement” was. a. Write your name with a marking pen on a large piece of paper. b. Write your name with a pencil or pen on a small piece of paper. c. Unbutton and rebutton the waist button on your jeans while wearing them. d. Untie and tie your shoes. e. Pick up a straight-backed chair. f. Pick up several coins. g. Pick up a drinking glass. h. Open and close a door using the doorknob. i. Try using chopsticks. j. Pick up and move several objects of various shapes and sizes. 3. Tape your thumbs to the palms of each of your hands with masking tape, as

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D ATA T A B L E Hands untaped

Task

Ease

Thumb involvement

Hands taped

Ease

Write name with marker Write name with pencil Unbutton and rebutton jeans Tie shoes Pick up chair Pick up coins Pick up glass Open and close door using knob Use chopsticks Pick up other objects:

4.

5. 6.

7.

shown in the illustration. You may need the help of a friend to wrap the tape around your second hand. Be careful not to wrap the tape so tightly that you cut off the blood circulation to your hand! Repeat the above list of tasks with your taped hands. Pay attention to any difference in the performance of the tasks. Enter your observations on the data table as before. Which tasks required the least “thumb involvement”? Which tasks required the most? Of the tasks you performed, which required fine motor skills (those requiring small subtle hand movements) and which required gross motor skills (those involving larger movements using arm and back muscles)? Is there a correlation between thumb use and the type of motor skills involved? Many scientists believe that the opposable thumb has helped humans adapt to their environment and survive. Using your data as a guide, explain some of the ways in which the use of the thumb enables humans to better survive in their environment.

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What’s Going On The least thumb involvement is required for writing with a marking pen on large paper, zipping, picking up the chair, using a doorknob, and moving small objects. The most thumb involvement is required for writing with a pen or pencil, buttoning the waist of your jeans, picking up coins, lifting a drinking glass, and using chopsticks. Those tasks that use fine motor skills tend to be the ones that also involve the thumb. Much human technological development has been directly linked to the thumb and the fine motor skills dependent on it. The use of tools and instruments, surgical skills, watchmaking, and any skill that requires manipulating small or very small objects, all depend on the use of the opposable thumb. Connections Only apes and primates have hands capable of grasping objects. The grasp is made possible by the opposable thumb, so called because it moves opposite to the rest of the fingers. In humans, the thumb can move farther across the hand than it can in any other primate. In this experiment, you compared your performance of a series of tasks using your thumb and fingers together with your performance of the same tasks without the aid of your thumb.

Safety Precautions READ AND COPY BEFORE STARTING ANY EXPERIMENT

Experimental science can be dangerous. Events can happen very quickly while you are performing an experiment. Things can spill, break, even catch fire. Basic safety procedures help prevent serious accidents. Be sure to follow additional safety precautions and adult supervision requirements for each experiment. If you are working in a lab or in the field, do not work alone. This book assumes that you will read the safety precautions that follow, as well as those at the start of each experiment you perform, and that you will remember them. These precautions will not always be repeated in the instructions for the procedures. It is up to you to use good judgment and pay attention when performing potentially dangerous procedures. Just because the book does not always say “be careful with hot liquids” or “don’t cut yourself with the knife” does not mean that you should be careless when simmering water or stripping an electrical wire. It does mean that when you see a special note to be careful, it is extremely important that you pay attention to it. If you ever have a question about whether a procedure or material is dangerous, stop to find out for sure that it is safe before continuing the experiment. To avoid accidents, always pay close attention to your work, take your time, and practice the general safety procedures listed below. PREPARE

• Clear all surfaces before beginning work. • Read through the whole experiment before you start. • Identify hazardous procedures and anticipate dangers. PROTECT YOURSELF

• Follow all directions step by step; do only one procedure at a time. • Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and first-aid kit. • Make sure that there is adequate ventilation. • Do not horseplay. • Wear an apron and goggles. • Do not wear contact lenses, open shoes, and loose clothing; do not wear your hair loose. • Keep floor and work space neat, clean, and dry. • Clean up spills immediately. • Never eat, drink, or smoke in the laboratory or near the work space. • Do not taste any substances tested unless expressly permitted to do so by a science teacher in charge. USE EQUIPMENT WITH CARE

• Set up apparatus far from the edge of the desk. • Use knives and other sharp or pointed instruments with caution; always cut away from yourself and others. • Pull plugs, not cords, when inserting and removing electrical plugs. • Don’t use your mouth to pipette; use a suction bulb. • Clean glassware before and after use. • Check glassware for scratches, cracks, and sharp edges. • Clean up broken glassware immediately. v © Facts On File, Inc.

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• Do not use reflected sunlight to illuminate your microscope. • Do not touch metal conductors. • Use only low-voltage and low-current materials. • Be careful when using stepstools, chairs, and ladders. USING CHEMICALS

• Never taste or inhale chemicals. • Label all bottles and apparatus containing chemicals. • Read all labels carefully. • Avoid chemical contact with skin and eyes (wear goggles, apron, and gloves). • Do not touch chemical solutions. • Wash hands before and after using solutions. • Wipe up spills thoroughly. HEATING INSTRUCTIONS

• Use goggles, apron, and gloves when boiling liquids. • Keep your face away from test tubes and beakers. • Never leave heating apparatus unattended. • Use safety tongs and heat-resistant mittens. • Turn off hot plates, bunsen burners, and gas when you are done. • Keep flammable substances away from heat. • Have a fire extinguisher on hand. WORKING WITH MICROORGANISMS

• Assume that all microorganisms are infectious; handle them with care. • Sterilize all equipment being used to handle microorganisms. GOING ON FIELD TRIPS

• Do not go on a field trip by yourself. • Tell a responsible adult where you are going, and maintain that route. • Know the area and its potential hazards, such as poisonous plants, deep water, and rapids. • Dress for terrain and weather conditions (prepare for exposure to sun as well as to cold). • Bring along a first-aid kit. • Do not drink water or eat plants found in the wild. • Use the buddy system; do not experiment outdoors alone. FINISHING UP

• Thoroughly clean your work area and glassware. • Be careful not to return chemicals or contaminated reagents to the wrong containers. • Don’t dispose of materials in the sink unless instructed to do so. • Wash your hands thoroughly. • Clean up all residue, and containerize it for proper disposal. • Dispose of all chemicals according to local, state, and federal laws. BE SAFETY-CONSCIOUS AT ALL TIMES

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